

ABSTRACT

A dual conduit drill string used in drilling holes for geothermal, oil and gas wells, and the like, comprises a removable inner conduit to permit the use of salvage or repair equipment within the outer conduit. The outer conduit comprises standard API drill pipe sections which are each slightly modified to receive the removable inner conduit sections. Each inner conduit section is provided with flexible hangers for suspending the weight of the inner conduit from a support ledge formed on the interior surface of the drill pipe. The hangers permit upward removal motion and rotation of the inner conduit with respect to the drill pipe, but prevent downward motion. Individual inner conduit sections are joined together at lockable stab joints in which locking is accomplished by the rotatable engagement of a key and locking socket. Preferably, the inner conduit is manufactured in uniform lengths and mounted in drill pipe sections of non-uniform lengths by means of drill pipe adaptor subs. In addition, a removal tool can be used to remove the inner conduit from the drill pipe by engaging the hangers of the lowest inner conduit.



